(1) Field of the Invention
The present invention relates to signal detection threshold circuits, and more particularly, relates to a system and method for automatically calibrating a signal detection threshold circuit.
(2) Description of the Prior Art
Signal detection threshold circuits are commonly used in receivers to prevent false signals from being detected by the receiver as a result of random noise. The signal detection threshold circuit determines whether the signals received are above a predetermined voltage or threshold setting. Only those signals of interest that exceed this threshold setting are passed on for detection by the receiver. Noise or other signals having an amplitude lower than the threshold setting are rejected by the signal detection threshold circuit.
Previously, technicians had to manually adjust receiver signal detection thresholds, and often the adjustment was made incorrectly. Setting the threshold too high caused a loss of sensitivity. In an early warning radar (EWR) system, for example, pulsed radio frequency (RF) signals will go undetected when the threshold is set too high. When the threshold is manually set too low, false signals are detected by the receiver due to random noise crossings.
This manual threshold alignment process was further complicated by the presence of signals in the environment. In some cases, radio frequency pre-amplifiers are remotely located from the receiver and outside signals cannot be isolated from the receiver detection circuits during calibration. This commonly occurs in military vessels and aircraft. In a submarine, for example, the pre-amplifier is often located in a periscope or an antenna mast close to the receiver antenna. Technicians must work around interfering signals to manually align signal detection thresholds in these systems. Manual alignment in such systems is time consuming and often results in an incorrect alignment and inadequate receiver performance.